Heretofore, among such type of electron beam accelerators the so-called weak convergence type electron synchrotron has been known. In the weak convergence type synchrotron, an inflector for guiding an incident electron beam onto an equilibrium orbit and an accelerating electrode for accelerating electrons on an equilibrium orbit are disposed within a magnetic field, and thereby it is attempted to reduce the size of the entire apparatus. Such weak convergence type synchrotrons can be utilized as lithography beam sources or the like by externally deriving radiant light generated by electrons on an equilibrium orbit.
However, in the case where an inflector and an accelerating electrode are disposed within a magnetic field, there is a shortcoming that a radiant light derivable scope in which radiant light can be externally derived is limited. Furthermore, since normally a beam diagnostic apparatus, a vacuum instrument and the like are also disposed in the radiant light derivable scope, partially the position where radiant light can be derived is limited to a very one part of the radiant light derivable scope.
One object of the present invention is to provide an electron beam accelerator in which the scope of the radiant light is enlarged so that the radiant light can be derived efficiently.